Adolescent and young adult women in the U.S., especially racial/ethnic minority and poor young women, have high rates of early and unintended pregnancy, which are associated with a host of adverse outcomes. While proximal and distal determinants of fertility have been widely studied, little research has focused on the role of stress in unintended pregnancy. Stress is a leading contributor to morbidity and mortality and a key mechanism that links social context and health disparities. The biological and psychological processes of stress may affect the pathways to unintended pregnancy, but this has not been addressed in reproductive health research. Moreover, how social determinants of stress shape young women's risk of unintended pregnancy is unknown. To improve our knowledge of the complex, interrelated determinants of unintended pregnancy and to advance reproductive health scholarship at the intersection of biological and social processes (i.e. biosocial), this K01 Mentored Research Scientist Development Award focuses on the important but understudied role of stress in unintended pregnancy during adolescence and young adulthood. So that I may conduct cutting-edge research in this area, I propose career development training to: 1) learn sociological theories, concepts, and methods for studying unintended pregnancy and stress; 2) build competency in bio demographic research methods and their application to fertility research; 3) attain a more nuanced understanding of the theory and research on the biology of stress and fecund ability; and 4) become proficient in advanced multilevel, longitudinal, and mediational statistical methods required for modeling the life course of and pathways between stress and unintended pregnancy. The corresponding K01 research project will: 1) estimate how trajectories of stress relate to unintended pregnancy; 2) investigate relationships between social determinants of stress (social stressors), stress trajectories, and unintended pregnancy; and 3) explore the biological processes (e.g., neuroendocrine, inflammatory, and immune) through which stress influences unintended pregnancy, during adolescence and young adulthood. To assist with the K01 training and research plans, I have assembled a strong multidisciplinary advisory board comprised of esteemed scholars, including mentor Jennifer Barber PhD, co-mentor Kathleen Mullan Harris PhD, scientific advisors Ana Diez Roux MD PhD, Timothy Johnson MD, and Julia Seng PhD MSN, and statistical consultant Yu Xie PhD. The University of Michigan Department of Obstetrics and Gynecology and Institute for Social Research and The University of North Carolina at Chapel Hill School of Public Health and Carolina Population Center will provide the infrastructures to support these activities. This K01 will establish me as an independent investigator poised to conduct new biosocial studies of fertility and ultimately lead innovative, interdisciplinary research efforts to improve outcomes an reduce disparities in young women's reproductive health.